19.1 Introduction

On December 24, 2008, a natural gas leak caused an explosion and fire. It killed one person and injured five others, including one firefighter and a utility worker. The explosion also destroyed one house completely and severely damaged two others adjacent to the destroyed house. Several other houses in the neighborhood were damaged. The neighborhood is located in Rancho Cordova, California. Pacific Gas and Electric Company, the utility owner and operator, operate 42% of California's natural gas pipe lines. According to Pacific Gas and Electric Company, the property damage was $267,000 (1–3).

The incident can be traced back to a phone call that Pacific Gas and Electric Company received on their Customer Contact Center Hotline at 9 : 16 AM. The phone call was made by a resident of 10716 Paiute Way who reported a gas odor outside of her house. The Customer Contact Center prepared a case ticket and contacted the Pacific Gas and Electric Dispatch Office as part of their normal procedures. A field technician received the message and headed toward Paiute Way to investigate the call. On arriving at the affected aforementioned residence, the technician's portable gas detector detected gas on her initial approach across the yard. The technician, equipped only with gas detectors suitable for indoor gas detection, contacted the dispatch office requesting equipment suitable for outdoor gas detection along with the assistance from the maintenance and construction department.

On meeting with the resident who had reported the leak, the technician learned that she also smelled gas at her neighbor's residence. The technician called her dispatch office to report the smell of gas at this new residence; they dispatched a field man, a leak investigator, and a foreman to the scene at 10 : 28 AM.

The technician then proceeded to 10712 Paiute Way. She did not detect any leaks inside the residence; however, the male resident of the house indicated that he knew where there was a natural gas leak in his neighbor's yard. He escorted the technician to 10708 Paiute Way. Once in the yard, the technician detected a strong natural gas smell originating from a small patch of dead grass.

The technician then proceeded to check the gas meters of all the houses along this stretch of Paiute Way. She did not detect any unusual gas meter readings that showed excessive gas flows. The technician then knocked on the door of 10708 Paiute Way. She did not receive an answer, so she parked her truck out front and waited for the arrival of the field man, leak investigator, and foreman.

The leak investigator needed to stop by the Pacific Gas and Electric service center to pick up the ionization detector (a type of detector used to locate outdoor natural gas leaks), but discovered a problem with his truck brakes. The leak investigator had to transfer all his equipment into another service truck delaying his departure by roughly an hour.

The foreman and leak technician finally arrived at Paiute Way 2 h and 47 min after the technician had requested the assistance from dispatch. The technician relayed the information she had gathered and then left the scene. The field man arrived shortly thereafter.

They proceeded to track down the location of the leak with the ionization detector. They reported a reading of 60,000 ppm, then 80,000 ppm, and finally, the device flamed out and sounded an alarm. This revealed that the gas-to-air mixture was so rich that it could not support a flame, indicating very strong amounts of natural gas. A man from the neighborhood informed them that he remembered Pacific Gas and Electric Company fixing a gas leak in this general area before. The Pacific Gas and Electric employees then noticed two sunken spots in the grass, indicating that the area had indeed been excavated sometime in the past.

At 1 : 35 PM, the leak investigator knocked on the door of 10708 Paiute Way (the house at which the technician could not earlier get an answer). After speaking with the residence of the house, the leak investigator closed the door and turned to head back to the leak when the house exploded. The explosion killed the resident and injured five others. The explosion was caused by gas leaking from the previous repair done by Pacific Gas and Electric Company in September 2006. The gas then migrated into the home at 10708 Paiute Way and ultimately exploded 2 years after the faulty repair.

These types of incidents are not all that uncommon. Natural Gas Watch listed the natural gas explosions in just 1 week in June 2011 (4). These were as follows:

• In Duluth, Minnesota, a contractor severed a natural gas line that forced the evacuation of hundreds of people from downtown Duluth for several hours on the afternoon of Thursday, June 9.
• An explosion leveled a house in Billings, Montana, on the morning of Wednesday, June 8.
• In Detroit, Michigan, a man was thrown through his front window when his house blew up on Friday, June 10. Authorities said preliminary reports indicate that the natural gas was the cause.
• In Noblesville, Indiana, a gas leak sent organizers scrambling to relocate the Noblesville Strawberry Festival after a natural gas leak was discovered on the site that had been chosen for the event on Monday, June 6. The leak's discovery also precipitated the evacuation of approximately 600 people, according to a story in the Indianapolis Star.

In the United States, they are far less common than in other countries. A sampling of some of the other recent natural gas explosions in other countries include the following:

• On Sunday, November 14, 2010, seven people, including a 9-year-old boy, were tragically killed in an apparent natural gas explosion at the Playa del Carmen resort in Mexico, according to media reports (5).
• On January 14, 2011, at least six people were killed and 10 injured in two separate household gas explosions in Russia on Monday. At least six people, including two girls, the first 4 months old and the second 6 years old, died after a household gas explosion in Russia's southern Stavropol Territory (6).
• Seven people were injured in a gas explosion in the Dnipropetrovsk region, eastern Ukraine, on Monday morning, February 8, 2010, Interfax Ukraine News Agency reported (7). The explosion occurred around 5AM at a two-storey apartment in Orzhonikitse, Dnipropetrovsk, according to the region's Office of Ministry of Emergencies. The injured have been hospitalized. One woman was in critical condition.

Risk assessment should be a major factor as communities plan for growth and development, as well as for planning for emergencies. Risks at the community level can include but are not limited to the following:

• chemical releases and catastrophic fires;
  • chemical plant and other process plant explosions,
  • train derailments,
  • truck accidents,
  • multiple structure fires,
  • wild land fires;
• natural disasters;
  • floods,
  • tornados,
  • hurricanes,
  • dust storms,
  • earthquakes,
  • high winds,
  • heavy snow and blizzards,
  • heat waves or extreme cold;
• transportation disruption;
  • highway accidents,
  • commuter train derailment,
  • transportation workers strikes,
  • power outages;
• widespread power outages;
• airplane crash;
• loss of employers;
• loss of workforce;
• loss of tax base.

A good example of a repeating natural disaster is the flooding of the Red River. The Red River that flows from North Dakota into Manitoba and regularly floods the towns of Fargo, ND; Oakton, MN; and Winnipeg, Manitoba, is a good example of river system where floods occur frequently. Major floods have affected the river system multiple times over the past 110 years. Most recently, floods have affected the city of Fargo, ND, in 1997, 2008, and 2011. However, residents continue to live in Fargo and businesses still remain open in the flood-prone areas (8).

Risk assessment techniques can and should be applied to the planning and development of communities to reduce the risks associated with natural and man-made disasters. The following section presents two examples of how these techniques can be applied to community planning to reduce the potential for disasters.